1. Technical Field
The present invention relates in general to generating power from a fluid source and, in particular, to an improved system, method, and apparatus for a linear hydraulic impulse engine for producing power via impulse fluid-driven translation.
2. Description of the Related Art
A substantial need exists for a means to produce power in an ecologically and economically sustainable manner. Hydraulic turbomachinery has seen widespread use for over a hundred years, but most conventional equipment is optimally suited for high head application, where environmental impacts may be severe. Equipment designed to produce power from low heads have typically been highly expensive, and unsuited for very low heads, such as settings with less than 3 meters of head. If a suitable low head hydropower technology was available, a large number of existing dams, used for non-power purposes such as flood control, navigation, and irrigation, could be retrofitted to provide renewable energy with minimal environmental impact.
Two main classes of devices for converting fluid motion into useful shaft work are reaction and impulse machines. Reaction machines utilize a pressure drop across the moving blades. In an impulse machine, the entire pressure drop occurs before the fluid interacts with the moving blade, so pressure is constant across the moving blades.
A favorable characteristic of impulse machines is their ability to maintain a consistent efficiency over a wide range of flow rates, without the need for complicated mechanisms to adjust blade or fluid angles. In contrast, the efficiency of reaction machines, such as propeller turbines, deteriorates rapidly as the flow rate deviates from the optimum, unless provisions are made to adjust the blade and/or fluid angles, such as is done with Kaplan turbines. Kaplan turbines utilize actuators to swivel the turbine blades as well as inlet guidevanes, to maintain high efficiency as flow rates change. However, these mechanisms significantly increase the cost of the turbines.
A common impulse machine is the Pelton turbine, which is commonly used to produce hydropower at high heads. The Pelton turbine is not used at low heads because it has a low specific speed. Another common impulse machine is the Cross-flow turbine, which can be used over a wide range of heads. However, the Cross-flow turbine is limited in size at low heads, and it must be carefully designed to avoid the situation in which the level of water in the tailrace or draft tube rises high enough to touch the blades, because efficiency would drop quickly under such a scenario.
Most turbomachinery in use utilizes a configuration in which a multitude of blades are attached to a single, central shaft. However, several devices have been conceived that utilize a form factor in which blades are mounted to a belt or chain and travel in linear paths around a pair of parallel axles. These devices may be referred to as “linear hydraulic machines.” A significant advantage of this form factor is that the cross-sectional area, which is rectangular, can be increased without affecting the radius of rotation of the blades. In this manner, a relatively large amount of flow can be utilized while independently controlling the rotational speed of the shafts, and the linear speed of the blades.
One such type of water-operative linear hydraulic machine is disclosed in Swiss Pat. No. 313850 to Eberhard. In that device the blades that contribute to power output travel in the same direction as the fluid flow 50% of the time and during such time contribute to power output. In the second operational stage they move counter to the direction of fluid flow. However, the efficiency of that apparatus is low because only one stage is utilized, and the second stage contributes to drag effects.
In U.S. Pat. No. 763,623 to Nance, the foils in the second stage are situated to receive direct input of fluid as well as fluid directed from the front foils after glancing off of them. Nance suffers from a turbulent confluence of the air that is influenced by one foil to the next foil, due to the disruption of the laminar flow of fluid. Nance further suffers in that the two streams of fluid, instead of working together and becoming confluent, are disrupted and agitated, causing a confused fluid environment when the two streams strike each other at the second stage.
Improvements to these older designs are disclosed in U.S. Pat. No. 4,049,300 to Schneider. However, the linear hydraulic machine described in that patent utilizes reaction foils, operating with the principle of lift. Because the moving foils in this system are asymmetrically shaped, only one stage of the foils can be optimally configured, without the use of complicated mechanisms to re-orient the position of foils in one stage versus the other. Thus, one objective of the present invention is to provide an improved system, method, and apparatus for a linear hydraulic impulse machine that performs well at low heads and is simple to manufacture.